Devices according to the preamble are e.g. known from EP 379 837 A1 and EP 340 550 B1.
In both cases the electrical heating elements are in an insulating frame, preferably made from plastic, to which is integrated or connected in fixed form a lamellar electrical conductor which directly contacts the heating elements. This arrangement is in the first case formed from a casing in the form of a U-shaped removal part, whose U-shaped legs directly contact the other side of the heating elements, and an insulating strip placed on the conductor. Pressing results from lamellae mounted on said casing. In the second document the casing is constituted by an electrically conductive profile tube, in which is placed the contact arrangement of PTC elements, conductors and insulating strips thereon, after which the casing is pressed. In said heating devices according to the preamble a joint action takes place on all the heating elements.
DE 199 33 013 discloses a heating device with plate-shaped heating elements, which in the extension direction of the heating elements and also the contacting conductor has two separately switchable heating zones. However, for this purpose the heating conductors have to be contacted from two front sides of the device or in each heating zone part of the heating elements must be omitted, so that the heating density or specific heating power is unnecessarily reduced.
Therefore the problem of the invention is to so further develop the heating devices according to the preamble that with an optimum, specific heating power all the heating zones only have to be contacted from one front side.